Sheet metal screws are designed for joining thin pieces of metal to wood, fiberglass or metal to metal primarily through a pre - drilled or own generated hole in light gauge metal. A sheet metal screw may be used in wood however a wood screw should not be used on metal. Sheet metal screws have sharp thread that cut into material such as sheet metal, plastic or wood. Their design makes it easy for them to tap into and tighten against whatever they are being installed into. Also called self-tapping